Vacuum pumps

ABSTRACT

A vapor vacuum pump includes an electrical vaporiser unit made of thin filaments of electroconductive material arranged to convey between them by capillary action the working liquid of the pump, for vaporization by heat generated by resistance of the filaments to passage of a current of electricity passing therethrough.

United States Patent Power [54] VACUUM PUMPS [72] Inventor: Basil DixonPower, Horsham, En-

gland v [73] Assignee: The British Oxygen 0 Company Limited, London,England 221 Filed: May21, 1970 21 App1.No.: 39,565

[30] Foreign Application Priority Data May 27, 1969 Great Britain.....,....26,829/69 [52] Cl. 219/271, 2l9/275,4l7/52,

[51] Int. Cl ..'.Q ..F22b H28 [58] Field of Search ..219/271, 274, 275,316, 307, 219/319, 352, 538-539; 417/51, 52,150, 152, 155, 154, 208;338/208 [56] 7 References Cited I UNITED STATES PATENTS 3,344,257 9/1967Moeller ..338/208 x 3,346,718. 10/1967 Cooleyetal ..219/319X 1153,686,474 1451 Aug. 22, 1972 2,140,516 12/1938 Cowan ..219/274 3,344,979,10/1967 Chester ..417/15 2,501,276 3/1950 .l-lickman ..417/1s2 FOREIGNPATENTS OR APPLICATIONS 814,547 6/1969 Canada ..219/3o7 96,788 12/1938016611361616, ..219/274 OTHER-PUBLICATIONS instant Hot Water Flows fromCold-Water Pipe, y 1

Popular Science July, 1961, pp. 44- 46 Primary Examiner-C. L. AlbrittonAttorney-Dennison, Dennison, Townshend & Meserole ABSTRACT A vaporvacuum pump includes an electrical vaporiser A unit made of thinfilaments of electroconductive -material arranged to convey between themby capillary action the working liquid of the pump, for vaporization byheat generated by resistance of the filaments to passage of a current ofelectricity passing therethrough.

8 Claims, 5 Drawing Figures Patented Aug. 22, 1972 3,686,474

2 Sheets-Sheet 2 VACUUM PUMPS Although described particularly withreference to oil as the working fluid, the vapor vacuum pump of thepresent invention could be used with water or even mercury as theworking fluid, if the problem of the electroconductivity of the liquidcould be overcome.

The present invention will now be described in greater detail by way ofexample with reference to the accompanying drawings, in which;

vacuum pump in which the warm-up time is considerably reduced comparedwith known pumps.

Accordingly the present invention provides a vapor vacuum pump which isas claimed in the appended claims.

By bundle in this specification is meant both a col lection or fascicleof filaments having its shape determined by external constraints, and anassembly of braided or interwoven filaments having a self-defined shape.I

The filaments may all be in parallel with each other and with thelongitudinal axis of the bundle, or they may be twisted or interwoven.The bundle may be formed of two ormore layers-of filaments, in which thefilaments in each layer are of different composition, structure orassembly. 1

The electroconductive filaments may be made of a resistive metal or ofinsulation material coatedwith resistive material. The electroconductivefilaments may be combined with non-conductive filaments in the samebundle, and the proportion, size or other parameters of thenon-conductive and/or electroconductive filaments can be chosen so thatthe composite bundle presents a'desired resistance of the flow ofelectrical current along the length of the bundle. By this means, whenelectric current is passed along the length of the bundle, Joule heat isreleased which is effective to vaporize liquid flowing along the lengthof the bundle.

The cross-sectional shape of the bundle is immaterial, althoughparticular shapes and configuration may be desired for someapplications.

. Because the filaments composing the bundle are fine, they present alarge surface area which is contacted by the liquid, so that when thesurfaces of the filaments become heated by Joule heating there is only arelatively small temperature difference between the surfaces of thefilaments and the liquid flowing along the bundle. In addition, theclosely spaced filaments provide a large number of capillary ducts whichextend partially or completely along the length of the bundle so as toresult in the rapid distribution through the bundle of the liquid to bevaporized. When capillary forces are relied on, then the degree ofcompaction of the bundle is such as to provide the required capillaryeflect while at the same time permitting the resultant vapor to pass tothe exterior of the bundle without applying disruptive forces to thebundle.

By a proper arrangement of the geometry of the bundle of filaments andthe rate of supply of the liquid, or other parameters, it is possible toachieve complete vaporization of the liquid within the bundle so thatthe vapor, in passing through the outer portions of the bundle beforeleaving the heating element, can be superheated to some extent, whichmight be advantageous in some applications.

FIG. 1 is a diagrammatic view of a vapor vacuum pump of the presentinvention in which, the bulk of the operating liquid is located remotelyfrom the vaporizer;

FIG. 2 is a diagrammatic view of a large second vapor vacuum pump of theinvention;

. siderable advantage that only-a small fraction of the FIG. 3 is adiagrammatic axial view of a helical vaporizer for use in the pump shownin FIG. 2;

FIG. 4 is a diagrammatic sectional view of a form of vaporizer which isan alternative to that form illustrated in FIG. 2 or FIG. 3, and

FIG. 5 represents axial sections of four different forms of vaporizerfor use in pumps of the present invention.

In the pump shown in FIG. 1, the vapor condensed on the inner walls of awater-cooled casing 2 flows into a reservoir 4 from which it flows at acontrolled rate through a valve 6 to a vaporizer 8 which is adapted tobe force-fed (in this case under the force of gravity) with the liquidto be vaporized. In this way a hydrostatic head is provided to carry theoperating liquid into the vaporizer 8.

The vapor produced by the vaporizer 8 is emitted from nozzles 10 and 12usual with vapor vacuum pumps. The vapor entrains molecules of the gasbeing evacuated from a system coupled to a flange 14 at the upper end ofcasing 2. After the vapor has condensed on the inner surfaces of casing2 the pumped gas leaves thepump by way of an outlet 16, which may beconnected to the inlet of a second pump (not shown) connected in cascadeand using the same or a different working fluid.

The pumps of the present invention have the conworking liquid is beingheated at any one time. This enables the pump to be fully operationalshortly after being energized, and to be opened to the atmosphere,-

without excessive degradation of the working fluid, shortly after it isdeenergized. This latter facility is particularly important in that itdispenses with the need for the isolation valve which is usuallyprovided for conventional vapor vacuum pumps. This is significantbecause such valves can cost as much as the pump itself.

In order to cool the pump quickly, the valve 6 is either opened fully toflood the vaporizer 8 with relatively cold liquid after the supply ofheating current has been stopped, or closed to stop further liquidreaching the vaporizer, closure taking place shortly before the flow ofheating current is stopped. With either mode of shut-down, the vaporizerstops emitting vapor relatively soon after the pump is deenergized.

' In the pump shown in FIG. 2, a vaporizer 8 is incorporated in a vapornozzle 18. Liquid to be vaporizer is v upper end of the vaporizer 8passes downwardly through it under both gravitational and capillaryforces. The vaporizer 8 is electrically heated, although the cables bywhich the heating current is supplied are omitted from the drawing forclarity. The resultant vapor issuing from the external surfaces of thevaporizer 8 emerges from the nozzle 18 through a discharge opening 24.In operation, the rate at which liquid is supplied to the nozzle isclosely related to the amount of electrical power supplied to it so thatvapor of the right quality emerges from the outlet 24.

The vaporizer 8 shown in FIG. 3 may be used to replace the longitudinalfilament type shown in FIG. 2. In FIG. 3 the bundle 26 of filaments isof rectangular cross-section and is wrapped in a helical groove in asupport 28. The base of the groove is in communication with an axialpassage 30 by a series of passages 32. Liquid enters the upper end ofthe axial passage 30 through an inlet 34 and then passes into theinterior of the bundle 26 through the passages 32. Although the passages32 communicate with the bundle at discrete intervals, capillary forcesare effective to saturate the bundle 26 uniformly with the liquid to bevaporized. By means which are not illustrated, current is passed alongthe length of the bundle 26. Either the bundle 26 is insulated from thesupport 28 or the support is of insulation material.

The vaporizer 8 shown in FIG. 4 is an alternative to that illustrated inFIG. 3. The main difference is that the cross-section of the bundle offilaments alters along the length thereof. Thus the liquid entering theinlet 34 passes into the splayed-out upper end of the bundle 26. Theoverall cross-sectional area of the bundle decreases as the liquiddescends so that the amount of heat released per unit volume of thebundle increases as the cross-sectional area of the bundle isrestricted. When the liquid is vaporized its volume increasesconsiderably and the splayed-out lower end of the bundle 26 enables thevapor to escape easily from the interior of the bundle without exertingdisruptive forces thereon. The vapor then emerges from the outlet 24 andfunctions conventionally. The means by which the bundle 26 is heated areagain not illustrated for clarity.

FIG. (a) shows an axial section of one form of vaporizer for a pump ofthe present invention. It includes two end plates 36 and 38 betweenwhich extends a plurality of parallel longitudinal filaments-40. Thebundle of filaments is constrained to be of cylindrical form for themajor portion of its length, but towards the bottom of the vaporizer thefilaments are splayed out.

' The splayed-out end 42 is provided to increase the spacing between thefilaments and thus enable the liquid to be vaporized to enter theinterstitial ducts more easily than if the lower end were kept tightlycompacted. Although it is difficult to illustrate, all the filaments 40are intended to be of electroconductive material, the plates 36 and 38acting as electrodes by which heating current can be passed along thelength of the bundle of filaments.

In the form of heating element shown in FIG. 5(b) (which, like FIGS.5(a) and 5(d) is a scrap sectional view of the cylindrical portion of abundle shaped similarly to that illustrated in FIG. 5(a)) theillustrated broken lines 44 are intended to represent filaments ofelectrical insulation material which are non-conducfilaments 44 which inturn is enclosed by a layer of conductive filaments 40.

In the arrangement shown in FIG. 5(d) the hollow A core 46 isv enclosedby a hollow cylindrical layer of conductive filaments 40 which isenclosed by a layer of non-conductive elements 44. Both the arrangementsshown in FIGS. 5(c) and 5(d) provide a passage by which liquid to bevaporized can conveniently be introduced into the interior of the bundleso that complete reliance is not placed on capillary forces to introducethe liquid into the vaporizer. V

For ease of illustration the filaments 40 and 44 in the vaporizersillustrated in FIG. 5 have been shown as being parallel to each otherand to the axis of the bundle. In practice the filaments could bearranged in'helically twisted layers of opposite hand, or given a simplehelical twist throughout, or be of interwoven construction. Any suitablearrangement can be used to retain the desired physical integrity of thebundle while providing a conductor of the desired cross-sectional areaand electrical resistivity.

One suitable material for the conductive filaments 40 is an electricalresistance wire such as Nichrome (trade mark). Suitable non-conductivefilaments can be of glass or other insulation material.

Any of the illustrated forms of vaporizer may be connected electricallyin series, but the inlet and outlet of the vaporizers are preferablyconnected in parallel between a-common source of liquid to be vaporizedand a plenum chamber or parallel arrangement of vapor nozzles. Such anarrangement permits a wide choice of systems for supplying heatingcurrent to the vaporizer while ensuring that each vaporizer functions asintended.

Pumps like that illustrated in FIG. 2 can .be arranged in many differentways which do not in themselves form part of the subject matter of thisinvention. In some cases more than one nozzle can be supplied from asingle vaporizer. In some cases it is preferable to use separatevaporizers (and possibly separate reservoirs) for pumping stages whichmay be connected to pump in series. This makes it possible to usedifferent pumping liquids in the various stages so that, for instance,the stage nearest the system being evacuated may employ less-volatileliquid (which is advantageous for. the

production of the lowest possible pressure), whereas the stage nearestthe pump outlet may employ a-morevolatile liquid, since this isadvantageous for compressing the pumped gases to the greatest possibleex- I tent before they are discharged from the system.

An advantage of the present invention is that it is necessary only forthe element itself and for a small quantity of liquid to be raised toboiling temperature. Because of the small mass to be heated, very rapidwarm-up is possible. Pumps can be designed so that only a low-massnozzle structure has to be heated by the vapor generated. Pumps can alsobe designed to stop emitting vapor very rapidly, by either continuing tosupply liquid after the heating current is stopped or stopping the flowof the liquid before the heating current is stopped.

Because of the very large surface area presented by the filaments, thetemperature difference between the filaments and the liquid flowingalong the capillary ducts formed by the interstitial spaces between thefilaments can be very small, while still enabling the required amount ofenergy to be transferred to the liquid. The heating elements can also bedesigned quite conveniently to provide a degree of superheating of thevapor by suitable choice of the various parameters of the heatingelement.

Iclaim:

l. A vapor vacuum pump including an electrically heated vaporizerpositioned remotely from a reservoir of working liquid and adapted to besupplied with the liquid under pressure, in which the vaporizer includesa bundle of thin filaments which are electro-conductive so that thebundle can vaporize liquid by Joule heat released over a very largesurface area.

2. A vapor vacuum pump as claimed in claim 1 in which the filaments arecompacted to define interstitial spaces therebetween and so that saidinterstitial spaces are longitudinally extending and are of size smallenough for the liquid to be vaporized to be drawn into the interior ofthe vaporizer at least partially by capillary forces.

3. A vapor vacuum pump as claimed in claim 2, in which the vaporizerincludes separate and contiguous layers of conductive and non-conductivefilaments.

4. A vapor vacuum pump as claimed in claim 3, in which the layers offilaments are circular or annular in cross-section.

5. A vapor vacuum pump as claimed in claim 3, in which thecross-sectional area of the bundle varies along its length.

6. A vapor vacuum pump as claimed in claim 1, in which the bundle has ahollow core into which is introduced the liquid to be vaporized.

7. A vapor vacuum pump as claimed in claim '1, in which the bundle offilaments is positioned in a helical groove in the surface of a supportof insulation material, the bundle being in communication at a pluralityof points spaced along its length with a hollow passage in the interiorof the support for the liquid to be vaporized.

8. A vapor vacuum pump as claimed in claim 1, in which the bundle offilaments is positioned in a housing having an inlet for liquid at oneend, and having an outlet for vapor at its other end.

1. A vapor vacuum pump including an electrically heated vaporizerpositioned remotely from a reservoir of working liquid and adapted to besupplied with the liquid under pressure, in which the vaporizer includesa bundle of thin filaments which are electro-conductive so that thebundle can vaporize liquid by Joule heat released over a very largesurface area.
 2. A vapor vacuum pump as claimed in claim 1 in which thefilaments are compacted to define interstitial spaces therebetween andso that said interstitial spaces are longitudinally extending and are ofsize small enough for the liquid to be vaporized to be drawn into theinterior of the vaporizer at least partially by capillary forces.
 3. Avapor vacuum pump as claimed in claim 2, in which the vaporizer includesseparate and contiguous layers of conductive and non-conductivefilaments.
 4. A vapor vacuum pump as claimed in claim 3, in which thelayers of filaments are circular or annular in cross-section.
 5. A vaporvacuum pump as claimed in claim 3, in which the cross-sectional area ofthe bundle varies along its length.
 6. A vapor vacuum pump as claimed inclaim 1, in which the bundle has a hollow core into which is introducedthe liquid to be vaporized.
 7. A vapor vacuum pump as claimed in claim1, in which the bundle of filaments is positioned in a helical groove inthe surface of a support of insulation material, the bundle being incommunication at a plurality of points spaced along its length with ahollow passage in the interior of the support for the liquid to bevaporized.
 8. A vapor vacuum pump as claimed in claim 1, in which thebundle of filaments is positioned in a housing having an inlet forliquid at one end, and having an outlet for vapor at its other end.